As the demand for high speed broadband networking over wireless communication links increases, so too does the demand for different types of networks that can accommodate high speed wireless networking. For example, the deployment of IEEE 802.11 wireless networks in homes and business to create Internet access “hot spots” has become prevalent in today's society. However, these IEEE 802.11-based networks are limited in bandwidth as well as distance. For example, maximum typical throughput from a user device to a wireless access point is 54 MB/sec. at a range of only a hundred meters or so. In contrast, while wireless range can be extended through other technologies such as cellular technology, data throughput using current cellular technologies is limited to a few MB/sec. Put simply, as the distance from the base station increase, the need for higher transmission power increases and the maximum data rate typically decreases. As a result, there is a need to support high speed wireless connectivity beyond a short distance such as within a home or office.
As a result of the demand for longer range wireless networking, the IEEE 802.16 standard was developed. The IEEE 802.16 standard is often referred to as WiMAX or less commonly as WirelessMAN or the Air Interface Standard. This standard provides a specification for broadband wireless metropolitan access networks (“MAN”s) that use a point-to-multipoint architecture. Such communications can be implemented, for example, using orthogonal frequency division multiplexing (“OFDM”) communication. OFDM communication uses a multi-carrier technique that distributes the data over a number of carriers that are spaced apart at precise frequencies. This spacing provides the “orthogonality” that prevents the demodulators from seeing frequencies other than their own.
The 802.16 standard supports high bit rates in both the uplink to and downlink from a base station up to a distance of 30 miles to handle such services as VoIP, IP connectivity and other voice and data formats. Expected data throughput for a typical WiMAX network is 45 MBits/sec. per channel. The 802.16e standard defines a media access control (“MAC”) layer that supports multiple physical layer specifications customized for the frequency band of use and their associated regulations. However, the 802.16e standard does not provide support for multi-hop networks that use relay nodes.
802.16 networks, such as 802.16j networks, can be deployed as multi-hop networks from the subscriber equipment to the carrier base station. In other words, in multi-hop networks, the subscriber device can communicate with the base station directly or through one or more intermediate devices.
The complexity involved in supporting multi-hop networks in a robust manner necessarily involves sophisticated control layer protocols. Such protocols do not exist. For example, as noted above, the IEEE 802.16e standard does not support multi-hop networks. The IEEE 802.16j standard for supporting multi-hop networks has been proposed, but the standard supports only a tree-based topology and does not provide good arrangements or methods for advanced topology support such as active and redundant path selection, i.e., path diversity, topology learning and congestion control for wireless communication from the mobile station to the supporting base station. As such, relay-based networks implemented under the existing IEEE 802.16j standard do not provide a reliable communication environment that can easily react to congestion and topology changes whether through the addition or subtraction of a relay node as part a normal business process or as a result of a failure or error condition within the network.
It is therefore desirable to have method and system that provides an arrangement to support such topology-related aspects of wireless networks that include relay stations. Such topology-related aspects include congestion control, topology learning and path diversity from the mobile station to the base station via relay nodes (also referred to herein as “relay stations”), including but not limited to those operating in accordance with the IEEE 802.16 standards.
Current IEEE 802.16 mobile stations are typically arranged to communicate using the IEEE 802.16e standard. As such, in order to maintain backward compatibility, relay stations configured to be serving stations (deliver/collect traffic to/from mobile stations) are arranged to transmit an 802.16e preamble to facilitate cell selection by the mobile station. However, a problem will arise in an environment in which relay stations are implemented in a wireless network that is arranged to support the desired topology-related aspects described above. For example, in order to support removal and addition of new relay stations, existing relay stations would need to monitor their operating environments to synchronize operation for path reselection. This would be done via monitoring preamble transmissions from neighboring relay stations. As such, a single radio relay node wanting to monitor preambles to support topology-related changes would stop its own IEEE 802.16e preamble transmission thereby adversely impacting the normal operation of supported mobile stations.
It is therefore also desirable to have a wireless communication network arrangement that allows relay nodes to both transmit and monitor preambles to support mobile stations as well as topology-related changes.